The cell is the fundamental structural and functional unit of all living
organisms. There are certain differences between the cells of different
living beings as well as the cells in the different part of the living
organism. All cells contain a fluid called cytoplasm and a nucleus, and
are enclosed in a cell membrane. Operations within the cells and the
coordination among various cells make the being live. The life of all the
living beings is, therefore, based upon the working of the cells.
The nucleus of a cell contains a chemical DNA
(deoxyribonucleic acid). All the instructions needed to direct the
activities of cell are contained within the DNA. DNA is a polymer The
monomer units of DNA are nucleotides, and the polymer is known as a
"Polynucleotide." There are four different types of nucleotides found in
DNA, differencing only in he nitrogenous base. The four nucleotides are
adermine (A), guanine (G) cytosine (C) and thymine (T). DNA from all
organisms is made up of the same chemical and physical components. The DNA
sequence is the particular side-by-side arrangement of bases along the DNA
strand (e.g. ATTCCGGA). This order spells out the exact instructions
required to create a particular organism with its own unique traits. The
DNA is normally in the form of a double strand (double helix) where the
second strand is complementary to the first strand. That is, in the second
strand a sequence such as AGCTTT is replaced by TCGAAA which carries the
The genome is an organismï¿½s complete set of DNA.
Genomes vary widely in size: the smallest known genome for a free-living
organism (a bacterium) contains about 600000 DNA base pairs, while human
and mouse genomes have some 3 billion. Except for mature red blood cells,
all human cells contain a complete genome.
DNA in the human genome is arranged into 24 distinct
chromosomes, physically separate molecules that range in length from about
50 million to 250 million base pairs. Each chromosome contains many genes,
the basic physical and functional units of heredity. Gregory Mendel was
the first to realize through extensive experiments with breading of peas
that at the lowest level, inheritance is binary, and that there is a
minimum unit of inheritance now known as a "gene". Genes are specific
sequences of bases that encode instructions on how to make proteins. Genes
comprise only about 2% of the human genome, the remainder consists of non
coding regions, whose functions may include providing chromosomal
structural integrity and regulating where, when and in what quantity
proteins are made. The human genome is estimated to contain about 30000
Gregory Mendel showed that the characteristics of
parents are passed on to their offspring through genes These genes might
produce visible characteristics in offspring, or might be carried for
possible transmission to another generation. The children of one set of
parents do not inherit all the same characteristics.
The union of two cells, the egg from the mother and the
sperm from the father is the beginning, of new individual. These two cells
like all other carry within them material that forms a definite number of
chromosomes. These chromosomes carry heredity factors or genes.
Chromosomes are pairs and each chromosome contain 1000 or so genes that
also occur in pairs.
The process of inheritance is based upon the process in
which the offspring receives one of each gene pair from each parent. Some
genes are dominant and some are recessive. An individual with dominant
gene, for a particular characteristic, displays that characteristic
whether only one or both genes in the pair are dominant. If a gene is
recessive, however, the characteristic associated with it does not show up
unless both genes in the gene pair are recessive. In case only one gene in
a pair is recessive, its effect will be marked by its dominant partner,
but the recessive gene may still be passed on to the individualï¿½s
offspring. Some characteristics are produced by a single gene or gene
pair. Whereas multiple ï¿½ factor inheritance involves the action of several
Genes are now known to be implemented as sequences of
genetic code that direct specific cells to produce a particular protein at
a particular time. An essentially infinite number of possible different
protein molecules can be produced depending on the particular order of
amino acid molecules used in their construction. The code for protein
production has been "broken" so that we now know that a three-letter
sequence (a codon) is used to specify a particular amino acid (there are
20 amino acids) For instance, the sequence GGC specifies that the amino
acid glycine is to be added to a protein molecule. Start and stop codons
mark the beginning and end of a protein coding sequence in a manner
startlingly like modern data communications schemes There are 64 possible
codons and only 20 possible amino acids so some redundancy and error
correction exists. The regulatory code sequences in genes that specify in
which parts of the body and/or at which times a protein will be produced
are much more complex and less well understood.
The genetic code has been compared to a blueprint
specifying the design of an organism. In fact the genetic code specifies
not only the design of the organism but provides for the mechanisms needed
to "read" the code and manufacture the components of the organism as well
as specifying the procedures needed for the life processes of the finished
organism. Simple organisms are completely defined genetically. Each tiny
nematode worm has exactly 958 cells. Humans, on the other hand, have
trillions of cells and 30,000 genes so the genetic code is more of a
general plan. For example, major blood vessels are genetically specified.
Everybody has an aorta. But minor blood vessels grow where needed
according to genetically defined rules.
Although all the somatic cells in an organism contain
the complete code, in any given cell only a relatively few genes are
active. The difference in the genes that are active determines the
difference between, say, liver and brain cells. A complex gene logic
determines when and where a particular gene will be "turned on". The gene
logic can accommodate varying amounts of positional detail. The gene logic
also controls when various activities will take place. Cells divide
rapidly in growing organisms but do not divide in adults unless needed to
replace dead or discarded cells. (Cancer involves a major breakdown in the
gene logic in which cells grow in both an inappropriate position and at an
inappropriate time. Cancer is thought to require multiple mutations, some
of which can be inherited.)
The early insight from Human DNA sequence is summarized below:-
1. Human genome contains 3 billion bases.
2. An average gene consists of 3000 bases.
3. The functions are unknown for more than 50% of discovered genes.
4. The human genome sequence is almost (99.9%) exactly the same in
5. About 2% of the genome encodes instructions for the synthesis of
6. Repeat sequences that do not code for proteins make up at least
50% of the human genome.
7. Repeat sequences are thought to have no direct
functions. But they shed light on chromosome structure and dynamics.
Over time more repeats reshape the genome by rearranging it, thereby
creating entirely new genes or modifying and reshuffling existing genes.
8. The human genome has a much greater portion (50%)
of repeat sequences than the mustard weed (11%), the worm (7%) and the
9. Over 40% of the predicted human proteins share
similarly with fruit-fly or worm proteins.
10. Genes appear to be concentrated in random areas
along the genome, with vast expenses of non coding DNA between.
11. Chromosome 1 (The largest human chromosome) has
the most genes (2968), and the Y chromosome has the fewest (231).
12. Genes have been pinpointed and particular
sequences in those genes associated with numerous diseases and disorders
including breast cancer, muscle disease, deafness and blindness.
13. Scientists have identified about 3 million
locations where single base DNA differences occur in humans. This
information promises to revolutionize the processes of finding DNA
sequences associated with such common disease as cardiovascular
diseases, diabetes, arthritis, and cancers.
Scientists suggest that the genetic key to human
complexity lies not in a gene number but in how gene parts are used to
build different products in a process called alternative splicing. Other
underlying reasons for greater complexity are the thousands of chemical
modifications made to proteins and the repertoire of regulatory mechanisms
controlling these process.
The HGP project is complete, many questions still
remain unanswered, including the function of most of the estimated 30000
genes. Researches also do not know the role of Single Nucleotide
Polymorphisms (SNPs), single DNA base changes within the genome or the
role of non-coding regions and repeats in the genome.
Mice and humans (indeed, most or all mammals including
Table 2: Comparative genome sizes of humans and other organisms.
cats, rabbits, monkeys and apes) have roughly the same
number of nucleotides in their genomes ï¿½ about 3 billion base pairs. This
implies that all mammals contain more or less the same number of genes.
Gene duplication occurs frequently in complex genomes;
sometimes the duplicated copies degenerate to the points where they no
longer are capable of encoding a protein. However, many duplicated genes
remain active and over time may change enough to perform a new function.
Since gene duplication is ongoing process, mice may have active duplicates
that humans do not posses, and vice versa. These appear to make up a small
percentage of the total genes, not larger than 1% of the total.
Nevertheless, these novel genes may play an important role in determining
species specific traits and functions.
What really matters is that subtle changes accumulated
in each of the approximately 30000 genes add together to make quite
different organisms. Further, genes and proteins interact in complex ways
that multiply the functions of each. In addition, a gene can produce more
than one protein product through alternative splicing or
post-translational modification; these events do not always occurs in an
identical way in the two species. A gene can produce more or less proteins
in different cells at various times in response to developmental or
environmental cues, and many proteins can express disparate functions in
various biological contexts. Thus subtle distinctions are multiplied by
the more than 30000 estimated genes.
Some nucleotide changes are neutral and do not-yield a
significantly altered protein. Others, but only a relatively small
percentage, would introduce changes that could substantially alter what
the protein does. Put these alterations in the context of known inherited
diseases, a single nucleotide change can lead to inheritance of sickle
cell disease, cystic fibrosis or breast cancer. A single nucleotide
difference can alter protein function in such a way that it causes a
terrible tissue malfunction. Single nucleotide changes have been linked to
hereditary differences in height, brain development, facial structure,
pigmentation and many other striking morphological differences ; due to
single nucleotide changes, hands can develop structure that look like toes
instead to fingers, and a mouseï¿½s tail can disappear completely. Many of
the average 15% nucleotide changes that distinguish humans and mouse genes
are neutral, some lead to subtle changes, where as others are associated
with dramatic differences. Add them all together, and they can make quite
an impact, as evidenced by the huge range of metabolic, morphological, and
behavioral differences we sea among organisms.
Although genes get a lot of attention, it is the
proteins that perform most life functions and even make up the majority of
cellular structures. Proteins are large, complex molecules made up of
smaller subunits called amino acids. Chemical properties that distinguish
the 20 different amino acids cause the protein chain to fold up into
specific three dimensional structures that define their particular
functions in the cell.
The constellation of all proteins in a cell is called
its proteome. Unlike the relatively unchanging genome, the dynamic
proteome changes from minute to minute in response to tens of thousands of
intra-and-extra cellular environmental signals. A proteinï¿½s chemistry and
behaviour are specified by the gene sequence and by the number and
identities of other proteins made in the same cell at the same time and
with which it associates and reacts. Studies to explore protein structure
and activities, known as proteomics, will be the focus of much research
for decades to come and will help elucidate the molecular basis of health
Most genes contain a switch called promoter. This
switch regulates the activities of the gene and decides when and how the
gene should become or not become active. An enhancer also works in the
gene. The promoter and enhancer work only when the transcription factors
responsible for mutation are operating. The genes are our active partners
and are sensitive to the changes taking place in our body and mind and
they register these changes by making suitable changes in their structure.
By channeling our thoughts in a specific direction the genes can be
changed, thus enabling us to progress in a desired way. This supports the
view that spiritual persons can increase their power by sacred thoughts
and determination. The genes are not our masters but are our servants,
they are governed by our thoughts and influenced by our environment.
Studies in behavioral genetics have shown that both
genetic and environmental factors influence the normal and deviant
behavior of human beings. Only a few decades ago, psychologists believed
that characteristics of human behavior were almost entirely the result of
environmental influences. These characteristics now are known to be
genetically influenced, in many cases to a substantial degree.
Intelligence and memory, novelty seeking and activity level, and shyness
and sociability all show some degree of genetic influence.
The principal role of genes in the chromosomes of human
has now been identified. Faulty genes in chromosomes lead to different
diseases as mentioned below.
Contains records of past lives. Faulty gene for GBA enzyme, which
breaks down certain fats, leads to Gaucherï¿½s, disease.
CH2: It contains the history of journey leading to
It has details of births in various species we
lived before. Faulty PAX ï¿½ 3 gene is associated with deafness and
color difference in eyes. This causes Wardenburg syndrome.
CH3: Contains evidences for the entire past history
in the form of genes. Faulty VHL gene causes abnormal blood vessel
formation. This gives von Hippel ï¿½ Lindau disease. The genes are
related to diabetes, obesity, etc.
CH4: This contains information about our future. It
also carries hints about forthcoming disease and traits. Faulty gene
causes dementia. This leads to Huntingtonï¿½s disease.
CH5: This is very sensitive to environment and
contains information about our immune system. It helps in study of
genetic disease like asthma, diabetes, etc. Faulty gene cause
malformed hands and feat. This leads to diastrophic dysplasia.
CH6: This is the intelligent chromosome, it is the
basis of our intelligence. It has been shown that in some cases
intelligence is hereditary. Faulty SCA1 gene causes clumsiness through
withering of the cerebellum. This leads to Spino-cerebellaratrophy.
CH7: It contains those characteristics which
determine our behavior as human being. This is regarded as the most
important chromosome. Faulty gene causes fatal build-up of mucus in
lungs and pancreas. This leads to Cystic fibrosis. Chromosome-7
contains genes related to William Neuron Syndrome which causes mental
disability and defiguring of face. They also influence leukemia, the
cancer of blood cells.
CH8: This contains information about our likings
and choices. Our habits and nature are stored and transmitted to next
life. This means that our merits and demerits are also influenced by
hereditary factors. Defective gene causes premature ageing. This leads
to Wernerï¿½s syndrome.
CH9: This determines the blood group. It also has a
role in disease we suffer. Skin cancer is more likely in people with
faulty CDKN2 tumor repressor gene. This leads to Malignant melanoma
CH 10: This chromosome contains the gene CYP17,
which produces an enzyme that converts cholesterol into harmones
called cartisol and Testosterone. These hormones produce stress in the
body. Defect in MEN2A gene causes tumors of thyroid and adrenal
glands. This leads to multiple Endocrine Neoplasia.
CH11: This contains genes which influence our
personality. Harvey RAS oncogene predisposes to common cancers. This
leads to cancer.
CH12: This is self assembled. Defects in PAH gene
causes mental retardation by blocking dygestion of common amino acid
in food. This leads to Phenylketonuria
CH13: Stores characteristics of
the past lives. Defects in BRCA 2 gene raises risk of breast cancer.
CH14: This is of indestructible nature. Faulty AD 3
gene is linked with the development of plaques in the brain. This
leads to Alzheimerï¿½s disease.
CH 15: Determines gender. Abnormal FBN1, gene
weakenes connective tissue potentially rupturing blood vessels. This
leads to Marfanï¿½s syndrome (position unknown).
CH16: This contains memory. Faulty PKD1 gene causes
cysts to form, which trigger kidney failure. This leads to polycystic
CH17: This determines the life span. Mutations in
P53 gene increase vulnerability to cancer. BRCA1 predisposes to breast
CH18: Helps in recovery from illness. Damage to
DPC4 gene accelerates pancreatic cancer
CH19: This determines fertility. Defective gene for
apolipoprotein raises blood cholesterol, predisposing to artery
blockage. This leads to coronary heart disease.
CH20: Abnormal adenosine deaminase (ADA) gene
destroys immunity. Correctable by gene therapy. This leads to severe
CH21: Wasting disease linked with defective
superoxide dismutase I (SODI) gene. This leads to Lou Gehrigï¿½s
CH22: This charactrizes freedom of thought.
Abnormal DGS gene triggers heart defects and facial changes. This
leads to DiGeorge syndrome. Chromosome-22 plays an important role in
immune system, mental disturbances and some types of cancers.
CH23: Abnormal DMD gene triggers muscle
degeneration. This leads to Duchenne muscular Dystrophy.
CH24: Governed by the gene for testis ï¿½
determining factor. This leads to Testicle development.